The present invention relates generally to solid state radiation detectors, and more particularly, to an improved Schottky barrier photovoltaic detector and a process for manufacturing it.
Schottky or surface barrier devices are basically a junction diode in which the junction is formed between a semiconductor material and a metal contact, rather than between dissimilar semiconductor materials. During the past few years, the technology for fabricating Schottky barrier devices has advanced at a rapid pace to the point where they are now used as elemental detection cells in large scale focal plane arrays. The individual Schottky barrier cells are generally formed at the junctions of platinum with a silicon base material.
The use of silicon-based material is a particularly desirable way to facilitate the manufacture of infrared focal plane detectors. In essence, the diodes are fabricated in high quality silicon wafers and are used to both create and store the optical signal. Attached to each detector is a charge coupled device (CCD) gate. The CCD gate provides a means for extracting signals from its associated detector and for conducting that signal from the semiconductor wafer to an associated video display device.
A major benefit derived from the use of silicon substrate material is the wealth of technological data available for constructing the aforementioned charge coupled diode units as well as the clock generators, drivers etc. necessary for sensing and processing the optical information stored in the Schottky barrier diodes. Another advantage is the cell-to-cell uniformity of Schottky cells formed of silicon material, such as has been heretofore observed in platinum-silicon cells.
The major objection to using silicon-based material for infrared imaging is that the elemental detectors do not have the sensitivity of detectors formed from other binary or ternary materials. For example, in the important 3.0 to 5.0 micrometer band, elemental detectors of ternary materials such as mercury cadmium telluride have theoretical sensitivities which are a factor of 10 times better than the best platinum-silicon detectors. Another disadvantage of platinum-silicon Schottky barrier diodes is their limited sensitivity at the high end of the aforementioned infrared band.